Ammonium sulfate recovery



AMMONIUM SULFATEv RECOVERY Filed June 4. 1945 MH/(E (/P Wwf/ l/VD Jie/4 mm /A/ ATTORNEY '-ful Vas fertilizer.

Patented Sept. 162V 1952 ff-:Sz': i f1- Merck & Co., Inc.,`Rahw ay, N. J., a corporationv l of New Jersey Application June 4, 194s, lserial V31,149

\ This invention relates `'to processes .for fthe recovery of chemical products from factorywaste liquors'. More particularly itrelates to processes for the recoveryvof sulfuric acid' and p-chlorobenzene sulfonic acidfrom residuesobtained in thevmanuf'acture of DDT. Sulfuricacid `is recovered in the form of-ammonium.sulfateuse- In the manufacture of DDT on a commercial scale there is obtained a substantial amount vof Vacidic Waste liquors having the following average composition.: 1

65 to 75% by Weight of Hz'SO4 '(100%) K 35-25% by Weight of p-chlorobenzene sulfonic acid 2% of organic'polymers o f :unknown structure Y The sulfuric `acid as Well as the pchlorobenzene sulfonic acid containedlin 'these'liquors are usually lost. Furthermorethe disposal of these liquors Vpresentsa serious diiiiculty due to the high acidity litation lies in the fact that the ammonium chloro- .benzene sulfonate is separated prior to crystallization of ammoniumsulfate. When carrying out my process o'n a commercial scale the saturated solution of ammoniums 'ulfate obtained instep 2 may be `recycled and used instep l; This saturated solution of ammonium sulfate may also be used in the neutralization step'wth ammonia, to' dilute the'mixture and to avoid the formation of a thick crystalline mass, which is diilicult to handle. While it is advantageous vto u sel partof thisdsaturated solution to 1 part o fwaste acid instep 1 sincefthepchlorobenzene sulforiic acid is least'solubleunder these conditions, it is preferable to vary fthe ratio 'somewhat by usingl to 2 volumes of saturated solution of ammoniumfsulfa'te to l volume of Waste'acicl in order to form a; precipitate which of these `liquors which require treatment with a neutralizingrv agent such asjlime or thev Ilike before discarding them 'into thesewer.'

'I'hav'e nowfound thatthe diiculty in disposing of the Waste liquors obtained in .connection with the DDT process may beovercomeandth'at the .content ofQsulfuric acid and p-chlorobenzene v sulfonic acid can be fully recovered.

,Inv accordancegwith my invention ,herein dis- ,.closed the Waste liquors .arev rst mixed vvith a saturated aqueous solution of ammoniumsulfate (step 1). Any suitable mixing `equipment vmay f be used preferably a tankprovidedwith mechanical agitation. The temperature' ofthe mixture Will'usually reach 100 C. or more.' The reaction mixture is then cooled to below 60 C.'Whereby' the vp-chlorobenzene sulfonic acid crystallizes out as the'ammonium salt almost quantitatively and may beremoved by filtration or any other suitable operation. The filtrate containing thevsulfuric acid essentially free of the impuritiesoriginally present in the Waste liquor is then neu` agents are required-for the carrying out of this pI'OCeSS.

The advantage in the Vstep 2 precipl can be handled by conventional factory equipment. I have found that if Vthe ratio is main- V tainedbetween 1 part of Waste acid to lvto 2Uparts of `the saturated solution, the 'p-chlorobenzene su'lfonic acidfwill becompletely precipitated 'as the ammonium salt, forming an easily -workable Acrystalline -niass.`A Thisfratio of the saturated solution may be changed if desired to suit l.the mechanical equipment employed. f A' The process maybe used ina kcontinuous manner. In-the diagram, s'te'p I represents essentially the treatment with a saturatedsolution of ammonium sulfate and step II neutralization with ammonia. "Both steps 'are exothermicand it'is necessary to use heat vvexchangers4 toi cool :the treated liquors'untilprecipitation occurs; It is also advantageous4 to adjust the ratio of waste liquor to the saturated'solution of ammonium sulfate in such a manner that thefprecipitation of arnrnoniin'nV p-chlorobenzene sulion'ate. 'is sub'- stantially complete While the crystalline mass is maintained in the form vof ia workable slurry. In carrying out the process on a large scale `and in a continuous manner it Will'be advantageous to use an excess of saturated solution of amr'nonium vsulfate'.(optin11um 3.42 to l'of'wasteracim The )filtratey obtained after lthe, 'removalof-` ammoniuil'nsulfate:in-fstepfl can be .usedwadvantageously. as fa :diluentin the neutralization with ammonia to minimize the formation of aha-rd mass4 yThus the process requires the use of-rconventional Afactoryequipment and onlyganhydrous gcomponents; sulfuric acid and; p-chlorobenzene sulfonic acid are recoveredfyvithoutappreciable Example 1 105 gr. waste DDT acid and 10o gr. of satirated aqueous (NH4)2SO4 solution (1:1 weight ratio) were mixed by pouring theA waste acidinto the ammonium sulfate solution, vunder moderate 4 A agitation. The reaction temperature reached 112 C. The ammonium p-chlorobenzene sulfonate started to crystallize upon cooling the mixture to 60 C. After cooling down to 25 C., the crystalsn were filtered off through a sintered glass lter funnel. Y The damp cake weighed 63.7 grams, and was only slightly hygroscopic, gaining 1.4 gr.`or 2.2% water during 48 hours at room temperature and .a relative humidity of iiD-100%.

l The crude ammonium salt of p-chlorobenzene sulfonic acid (63.7 gr.) was washed with 50 gr. of saturated aqueous ammonium sulfate solution at C. A thin slurry resulted, which was iiltered and sucked on vacuum for 10 minutes. The

.damp cake now weighed 5l gr., which shows a lossof 13.7 grams. The ltrate from the pre- .cipitated hydrate, weighing 137.6 gr. (sp. gravity 1.447 at 27 C.), was neutralized with anhy- -drous ammonia at 40-60l C. No water was added during neutralization, the reaction mix- 'ture forming a stiff but still workable slurry of snow-white ammonium sulfate crystals. Beginning at pH 1.8, a brownvcolor (probably due -to organic impurities) became evident, and the pH quickly reached l8.5. The slurry was cooledv -to 25 C.vand filtered. Some color came through -in the iiltrate. -The wet cake weighed 101.4 gr., Y after being firmly pressed and allowed to remain on funnel under vacuum for 10 minutes. Upon drying at 110 C. for 16 hours the dry solid weighed 87.8 gr. It was easily pulverized, had a -flnal very pale cream color and a pleasing aro- -vmatic odor. Anelemental analysis on a portion .of this dried ammonium sulfate showed a con- ;tent of 0.49% C, 5.13% H and less than 0.2% Cl. -These values represent an organic impurity (calculatedas the ammonium saltofp-chloroben- -zene sulfonic acid) `of 1.0 to 1.2% by weight.

71% H2804 25% p-chlorobenzene sulfonic acid K 3.5% H2O 0.5% DDTv A 645 cc. (1076 grams) of the above waste acid were mixed with 783.6 gr. of a saturated aqueous (NH4):SO4 solution. This corresponded to a 1:1 lvolume ratio of waste acid and ammonium sulfate.

The temperature of the mixture rose to 116 C.

On cooling, ammonium p-chlorobenzene sul- ,1

fonatejstarted to crystallize out at 65C. The hygroscopic, sandy-colored flakes were iltered cih-weighing 460.7 grams."

klnonium sulfate.

Aplished in one step.

This represents a recovery of 0.428 lb. of ammonium-p-chlorobenzene sulfonate per pound of waste acid.

Anhydrous ammonia was bubbled through the filtrate. Ammonium sulfate crystals were formed immediately. Upon agitation, the temperature rose to 87 C. and the batch became so heavy with crystals that it had to be filtered. The pH of the filtrate was 1.0-which indicated that it was strongly acid and far from being neutralized. This filtrate wasl ammoniated again until it became diicult to handle, due to the thick slurry 1 of crystals formed. The filtrate from this second batch was again acid (pH 2.2), and was ammoniated again until a pH of 9.3 was attained.

The total yield of ammonium sulfate obtained was 0.9 lb. per pound 'of waste acid.

Example 3 The same amounts of waste acid and ammonium sulfate were used, as in the preceding example. However, the ammonium sulfate solution was made up by using 121.5 grams of the ammonium *sulfate cake obtained in the third batch of Example 2. A total of 11.6% of the ammonium sulfate obtained in Example 2 was used as recycle solution," to be reacted withthe Waste DDT acid. Considerable foaming occurred on increasing the agitation of the mixture above a certain point. The temperature rose to 112 C. Upon cooling to 25 C., 509.1 gr. of ammoniump-chlorobenzene sulfonate was obtained in crystalline form. This represents a recovery of 0.463 lb. of ammonum-p-chlorobenzene sulfonate per pound of waste acid used.

Ammonia was bubbled through the filtrate, until a pH of 6.8 was reached. The temperature rose to 82 C. The ltrate in this 'case was ammoniated completely in one batch, and the'crysjtal slurry formed was so thick that the batch ,fa'te per pound of waste acid was obtained.

The 1:1 volume ratioof waste Yacid to ammonium sulfate, .although giving the best recov- `ery of p-chlorobenzene sulfonic acid, is not recommended for practical reasons due to the extreme thickness of the ammonium sulfate slurry formed in the ammoniation step. This slurry .can be handled only with vdiiliculty, as the batch becomes almost completely solid upon neutralization of the acid with ammonia. Also, a .1:1 ratio would lead to formation of ammonium sulfate-sulfuric acid complexes, instead of pure am- Therefore, a weight ratio of 3.42:1 (or greater) of saturated ammonium sulfate to spent acid is recommended for practical purposes.

Such a. 3.42:1 ratio would give an ammonium Ysulfate substantially free from occluded H2504 Vand complex salts, and a slurry which can `be easily handled when neutralization is accom- The results of. Example 2 and 3 may be summarized as follows: Y

1 c l l Percent Acid ionate reacted recycle Exe; 1076.0 160.7 '1048.6 148.0 11.6 Ex.3.. 1096.7V 509.1 1129.0 `221.0 l 111.0

Yields-per pound of waste acid (in 1bs.):

Modications may be made in carrying out the present invention Without departing from the spirit and scope thereof, and the invention is to be limited only by the appended claims.

I claim: l

1. The process for the recovery of ammonium p-chlorobenzene sulfonate and ammonium s ulfate from factory waste acid containing p-ch'lorobenzene sulfonic acid and sulfuric acid, which comprises mixing one volume of said Waste acid with at least an equal volume of a saturated aqueous solution of ammonium sulfate, separating the solid ammonium p-chlorobenzene sulfonate precipitated from said mixture, neutralizing the resulting solution With ammonia, and recovering ammonium sulfate from the neutralized solution.

2. The process for the recovery of ammonium p-chlorobenzene sulfonate and ammonium sulfate from the waste sulfuric acid obtained in the manufacture of DDT which comprises mixing one volume of said Waste acid with at least an equal volume of a saturated aqueous solution of ammonium sulfate, separating the solid ammonium p-chlorobenzene sulfonate precipitated from said mixture, neutralizing the resulting solution with ammonia, and recovering ammonium sulfate from the neutralized solution.

3. The process for the recovery of ammonium` p-chlorobenzene sulfonate and ammonium sulfate from the Waste sulfuric acid obtained in the manufacture of DDT which comprises mixing one volume of said Waste acid with 1 to 3 volumes of a saturated aqueous solution of ammonium sulfate, separating the solid ammonium p-chlorobenzene sulfonate precipitated from the mixture, neutralizing the resulting solution with ammonia, and recovering ammonium sulfate from the neutralized solution.

4. The process for the recovery of ammonium p-chorobenzene sulfonate and ammonium sulfate in a continuousl manner from the Waste acid obtained in the manufacture of DDT, which comprises mixing onevolume of said waste acid with at least one volume of a saturated aqueous solution of ammonium sulfate, separating the solid ammonium p-chlorobenzene sulfonate precipitated from said mixture, neutralizing the resulting solution with ammonia, recovering ammonium sulfate from the neutralized solution,

and recycling the ammonium sulfate mother liquor to precipitate the p-chlorobenzene sulfonate from another batch of Waste sulfuric acid liquor.

5. In the process for the recovery of ammonium p-chlorobenzene sulfonate from Waste sulfuric acid obtained in the manufacture of DDT, the step which comprises mixing one volume of said waste acid with at least an equal volume of a saturated aqueous solution of ammonium sulfate, and separating the solid ammonium pchlorobenzene sulfonate precipitated from the mixture.

RANALD G. DUNNING.

REFERENCES CITED The following references le of this patent:

AUNITED STATES PATENTS OTHER REFERENCES Ind. and Eng. Chem., pp. 916-922, September 1946, v01. 38, No. 9.

are of record in the 

1. THE PROCESS FOR THE RECOVERY OF AMMONIUM LP-CHLOROBENZENE SULFONATE AND AMMONIUM SULFATE FROM FACTORY WASTE ACID CONTAINING P-CHLOROBENZENE SULFONIC ACID AND SULFURIC ACID, WHICH COMPRISES MIXING ONE VOLUME OF SAID WASTE ACID WITH AT LEAST AN EQUAL VOLUME OF A SATURATED 